1. Field of the Invention
The present invention relates to exposure control apparatus for use in a copier or the like, and more particularly to exposure control apparatus in which the intensity of the light from an exposure lamp is sensed to produce a detection signal and the current supply to the exposure lamp is regulated according to the detection signal thereby maintaining the light intensity at a determined level.
2. Description of the Prior Art
The lamp for illuminating an original document, used in the copier or the like, should preferably have a constant light intensity, as otherwise it becomes not possible to obtain a copy with a desired density, or to maintain a constant density in a series of copies from the same original document. In order to obtain a constant intensity there is known a control method of maintaining a constant supply voltage to the lamp. However the lamp luminance is influenced by external conditions such as temperature and cannot be maintained constant simply by the constant supply voltage. It can therefore be considered to detect the luminance of a fluorescent lamp and to accordingly control the voltage supplied to the fluorescent lamp thereby maintaining a constant luminance thereof. However, even when a desired luminance is obtained after the start of power supply, it is not easy to achieve a constant luminance because of the associated factors such as the circuit response or afterglow of the lamp.